As well as affecting spacecraft, the gravitational influence of planets also affects the distribution of asteroids and comets. There are families of small bodies, for example the Apollo and the Plutino asteroids, which converges on a particular shape and size of orbit because their members have been repeatedly subjected to small gravitational attractions from the planets.

There are also individual, one-off gravitational effects that can send objects such as comets either plummeting into the inner Solar System or hurtling out beyond the planets. Watching for these ‘wild cards’ is a prime area of study for ESA, as the geological record on Earth shows that asteroids have occasionally collided with our planet in the past.